The present invention relates to a fluid controller comprising a valve element which is movable upward or downward by rotating a valve stem to open or close a fluid channel.
With fluid controllers of the type mentioned, the valve element is movable upward or downward by rotating the valve stem to move the stem upward or downward. The valve element is brought into contact with and seated in a valve seat to close a fluid channel by being moved downward. The valve element is brought out of contact with the valve seat to open the fluid channel by being moved upward. The valve stem and the valve element are provided as separate members, and the lower end of the stem is rotatably attached to the upper end of the element so that the valve element will not rotate with the stem when coming into contact with the valve seat.
However, when the valve stem is rotatably attached to the valve element, an upward or downward backlash (play) inevitably occurs therebetween, consequently entailing the following problem.
Fluid controllers include those wherein the valve element bites into the valve seat with a wedge effect when seated in the seat to completely close the fluid channel. The smaller the cone angle of the valve element, the greater is the wedge effect and the greater is the likelihood of the valve element biting into the seat. When the biting of the valve element occurs, the valve element remains biting in the valve seat without moving upward even if the valve stem is rotated from the completely closing position toward an opening direction, until the stem moves upward by an amount corresponding to the backlash between the stem and the element. It is when the valve stem has moved by a greater amount that the element comes out of contact with the seat. The moment the valve element leaves the seat, the element is pushed toward the valve stem by the pressure of fluid and thereby moved upward by an amount corresponding to the backlash to strike against the stem. The same phenomenon as above occurs also in the case of valves having bellows or diaphragm incorporated therein. Accordingly, the striking contact of the valve element with the valve stem gives off a noise, causing the user discomfort. Further especially when the fluid controller is used for controlling the rate of flow, extreme difficulty is encountered in finely adjusting the flow rate between the fully closed position and a slightly opened position.